This invention relates to apparatus and methods of testing display systems.
The invention is more especially, but not exclusively, concerned with apparatus and methods of testing systems which include cathode-ray tube displays such as for example, some aircraft head-up display systems.
To ensure accuracy in reading a display system it is necessary to calibrate or adjust it by observing its response to signals of known value. This is done, for example, with a pointer instrument, by supplying a known voltage across the instrument and having an observer note the deflection of the pointer. The observer determines the error in the deflection and calculates the adjustment that is required to be made to the instrument to correct for this error. In a cathode-ray tube display system arranged to display a line symbol, it may be necessary to determine the size of the symbol, the line width, the orientation of the line and its location, and the brightness of the symbol. In, for example, a head-up display system where the image on a cathode-ray tube is focussed at infinity, it is necessary to determine the disposition of the image in terms of angles subtended at the observer. At present this is done by rigidly mounting the display unit and by measuring angles with a theodolite that is rotated to align with the image. The orientation of the theodolite is noted by the observer and calculations made to determine any adjustments that may be needed to be made to the unit.
As can be appreciated, these manual methods of testing are lengthy and tiresome especially in the case of head-up display systems.